J. Electrochem. Sci. Eng. 2(2) (2012) 53-66; doi: 10.5599/jese.2012.0011
Open Access : : ISSN 1847-9286
www.jESE-online.org
Feature article
Electrochemical Engineering - its appearance, evolution and
present status. Approaching an anniversary.
VELIZAR STANKOVIĆ
Department of Metallurgical Engineering, Technical Faculty Bor, University of Belgrade, Serbia
E-mail: vstankovic@tf.bor.ac.rs
Received: April 10, 2012; Published: MMMM DD, YYYY
The goal of electrochemical engineering is to achieve
in a quantitative way an optimal cell design
N. Ibl
Abstract
Through this story an attempt has been made to present a chronology of
electrochemical engineering - from its appearance as an individual science, via its
growth throughout the five decades of its existence as an individual science, until today.
The collaboration and linkage of electrochemical engineering with other disciplines has
also been discussed in this essay. The role and duties of electrochemical engineering in
the 21st century have been touched upon to the extent that it was possible.
Keywords
Electrochemical engineering, Electrochemical reactors, Cell productivity, Education in
electrochemical engineering
1. Circumstances of the emergence of electrochemical engineering as a new scientific discipline
The term “electrochemical engineering“ first appeared in the literature as a novel title of the
fourth edition of C.L. Mantel’s book Industrial Electrochemistry [1], published in 1960 (the first
edition was published in 1931 and later editions in 1940 and 1950). Just looking through its
contents, one can easily realize that this book mainly describes the electrochemical technologies
for production of some particular electrochemical products. Although there was an attempt to
group and systematise the exposed technologies in separate chapters, such as: basic
electrochemical relationships and laws; molten salt electrochemistry, metal electrowinning and
electrorefining; gases production; corrosion and electroplating, a big gap still remained between
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ELECTROCHEMICAL ENGINEERING - ANNIVERSARY
the title and the contents. This book, along with others relating to industrial electrochemistry from
around that time, demonstrated that, at the end of the ‘50s, the number of electrochemistry
technologies had expanded to the extent that it was not possible even to describe each of them in
a textbook without a lot of repetition in describing each technology. This made books more and
more voluminous, making it troublesome for students, who had to learn each technology for the
production of every particular electrochemical product. This was one of the reasons, maybe not
the most important but still a very serious one, for starting to consider establishing a new
discipline in a similar manner to what had been done when chemical engineering appeared at the
end of the 19th and the very beginning of the 20th century - firstly through unit operations and
afterwards through transport phenomena and reaction engineering. Hence, at the end of the ‘50s
and in the early ‘60s, chemical engineering had already developed its capabilities to treat unit
operations and processes in a way that interconnects physical and physico-chemical phenomena
with chemical processes to chemical technology.
At that time (the end of the ‘50s), it became evident that similar transformations to those that
had occurred in chemical technology had to be implemented in industrial electrochemistry to get
more engineering and a more scientific approach to improving the existing technologies and
establishing new ones. By then, almost all that had been achieved in improvements to any
electrochemical technology was due to the art of engineering rather than to an applied science.
2. Interconnection between chemical engineering and electrochemistry - pioneering works
linking the two sciences
During the ‘50s a close interconnection between electrochemistry and chemical engineering
was established, on a theoretical level, through the penetration of electrochemistry into chemical
engineering and vice versa. During that period, firstly C.S. Lin with his co-workers [2], and shortly
afterwards Tobias, Eisenberg and Wilke [3] considered, both experimentally and theoretically, the
mass transfer phenomenon of ions coming from the bulk electrolyte to the electrode surface by
molecular diffusion, migration and convection. Their considerations resulted in the well-known
equation connecting limiting current density with the other variables affecting it:
iL  kL zFcb
(1)
Where: iL - is limiting current density; kL - mass transfer coefficient; z - number of exchanged
electrons in electrochemical reaction; F – Faraday’s constant; cb – bulk concentration of reacting
ions, all given in arbitrary units.
The published papers in which an electrochemical method of limiting current measurement was
used to evaluate the mass transfer coefficient at convective mass transport forged a strong
connection between electrochemistry and chemical engineering. The few early works [2,3] relating
to local limiting current measurements had opened new opportunities – employing
electrochemical methods for evaluation either local or overall, as well as instantaneous or timeaveraged transport characteristics of flowing liquid systems, e.g. to quantify mass, heat and
momentum transfer features. In this way, methods of adsorption, dissolution, or sublimation used
till then for evaluation of the mass transfer coefficient, were replaced by a much faster and more
reliable electrochemical method of the limiting current measurement and computation of a mass
transfer coefficient from experimentally recorded polarization curves, using Eq. (1). This method
was widely exploited during the ‘60s and particularly the ’70s, until today, for studying the mass
transport rate in different electrochemical model-systems. The electrochemical method of limiting
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current measurement, in its early or advanced form, contributed greatly towards providing
evidence about the hydrodynamic image of flowing systems. Thanks to the Chilton-Colburn
analogy widely used at that time in transport phenomena, data obtained for local or overall mass
transfer coefficients were then employed to estimate heat transfer as well as momentum transfer
in similar flowing systems. Indeed, these works confirmed the great influence of flowing conditions
in electrochemical reaction rate via mass transport in electrochemical reactors, opening up a new
research area for creating new, or improving the existing electrochemical cells.
In that period (the middle of the ‘60s), the method of conductivity measurement was also
introduced in chemical engineering for local or overall porosity measurement in liquid fixed or
fluidised beds and later for a gas hold-up quantification in gas-liquid systems, regardless of
whether gas is dispersed in a liquid phase, or generated therein due to a chemical or
electrochemical reaction.
This close collaboration between electrochemistry and chemical engineering also had a reverse
direction – bringing benefits for electrochemistry. The marker pulse technique, a method widely
used in chemical engineering for axial and radial dispersion measurement of a tracer in a reaction
chamber, was adopted and modified at the end of the ‘60s, to be used for investigation of ionic
species distribution, generated in a flowing electrolyte in electrochemical reaction systems. At that
time, terms like “plug flow reactor” or “perfectly mixed reactor” were reserved for chemical
and/or catalytic reactors, but not yet used for electrochemical cells.
Mass transfer in a cell when changing the hydrodynamic conditions was investigated at that
time as a method for mass transfer enhancement when a diffusion-controlled electrochemical
reaction takes place. The use of dimensional analysis and similarity theory adapted for and applied
in chemical engineering, was at that time introduced in electrochemical studies in order to
minimize the possible combinations of operating variables that have to be tested in the research
and development of new electrochemical processes, new electrochemical reactors, or new
technologies. This was very important in the scaling of laboratory results to the pilot-plant and
then from pilot data to the industrial scale. The experimental data obtained were then expressed
in the form of dimensionless relationships, either as:
Sh = f(Re, Gr, Sc, Fo, Γ1, …Γn)
(2)
or, based on the Chilton-Colburn analogy, as:
ffr/2 =jh = jD = f(Re),
(3)
describing mass, heat and momentum transfer. Equations like these had been introduced as a tool
in the consideration of diffusion-controlled electrochemical reaction systems and published at that
time in the literature. In equations (2) and (3) Sh is Sherwood number; Re – Reynolds number; Gr –
Grashof number; Sc – Schmidt number; Fo – Fourier number; Γi – dimensionless groups dictated by
geometric similarity; ffr – Fanning friction factor; jD, jh – mass and heat transfer factor, respectively.
Moreover, new similarity criteria, like the Wagner number (Wa), relating particularly to the
nature of electrochemical reaction systems, were derived and introduced in dimensionless
expressions similar to equations (2) and (3).
Obviously, both sciences – electrochemistry and chemical engineering - profited from their
mutual collaboration during the ‘50s and ‘60s.
The main benefit from this interrelation between electrochemistry and chemical engineering
was the appearance of a new discipline – named electrochemical engineering.
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ELECTROCHEMICAL ENGINEERING - ANNIVERSARY
3. Establishing electrochemical engineering on the scientific scene
In the early ‘60s, as a result of the interrelation between chemical engineering and
electrochemistry, numerous qualitatively new papers appeared in the relevant literature (mainly
in chemical engineering rather than in electrochemical journals), founding the conditions for the
appearance of a new multi-disciplinary science – electrochemical engineering.
C. Wagner, V.G. Levich, N. Ibl, C. Tobias, P. Le Goff, and J. Newman with their collaborators, as
well as some others not mentioned here due to limited space, contributed a lot to the
establishment and early development of the new discipline. These scientists may be considered as
the founders of electrochemical engineering - a separate scientific discipline born from the mutual
influence of chemical engineering and electrochemistry. Wagner first introduced the name to this
discipline, publishing a paper in the second volume of Advances in Electrochemistry and
Electrochemical Engineering in 1962, entitled “The Scope of Electrochemical Engineering” [4]. In
that article, Wagner makes a clear distinction between electrochemical engineering science and
electrochemical engineering technology.
In the middle of the 20th century there were not so many electrochemical technologies. From
this time-distance, we might suppose that improvements of these technologies, starting from their
appearance, occurred little by little through decades, more by intuition or by trial and error than
by a scientific approach to basic phenomena affecting features of these processes. The
contribution of electrochemical engineering, in its early stage (at the beginning of the ‘60s), to the
design of industrial electrochemical cells and processes was very modest - almost negligible. Mass
transfer considerations in electrochemical reactors had an academic rather than an engineering
approach. This was mainly because there was no mass transfer limitation when the process
operated with electrolytes having high concentrations of reacting ions, as was mostly the case
with industrial electrochemical processes from that period. Current density distribution was not of
major importance in those cases and for the side by side electrode configuration that was mainly
used in electrochemical cells from that time. The operating current density was not limited by
diffusion of reacting ions, but more by the cell voltage and consequently the specific energy
consumption than by mass transport limitations or irregular current distribution.
At that time, electrochemical reaction engineering was a term of no significance for industrial
practice. It was enough to find empirically the cell volume and inter-electrode distance needed to
estimate the highest degree of conversion and the highest current efficiency at the lowest cell
voltage. Not much attention was paid to enhancing the cell productivity by changing either the
hydrodynamics conditions in a cell or the cell voltage in order to get optimal operating energy
conditions.
A great step towards new cell design and its optimisation was made when the pioneering work
of Jottrand and Grunhard [5] appeared in 1962, concerning the mass transfer enhancement in a
tubular cell with a fluidised bed of inert particles in the inter-electrode space. Very soon after,
numerous articles on the same subject but with different aims were published in the literature,
providing evidence on how many times various inert turbulence promoters (ITP), placed in interelectrode space in a cell, enhance the limiting current density due to an increase in the mass
transfer coefficient. Besides higher cell productivity, a smoother electrode surface was obtained in
the case of either metal deposition or dissolution, so that these types of cells were further
developed with the aim of employing them in electroplating, electro-polishing, electroforming and
other similar processes of electrochemical surface treatment, but also for metal removal from
various sources. Several years after this series of articles, a new type of cell with expanded mesh
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electrodes, in which mass transport is facilitated by a fluidised bed of glass beads, was developed,
and later marketed by BEWT engineers, UK, as a “Chemelec cell” for the recovery of metals from
wastewaters and industrial effluents.
At that period (the second half of the ‘60s), a new electrochemical reactor also appeared,
named the three-dimensional electrode cell (TDE-cell). The first articles on this subject were
published at the end of the ‘60s and early ‘70s by English scientists from Newcastle and
Southampton Universities and shortly afterwards by French scientists from the University of
Nancy, as well as by German scientists from DECHEMA Institute.
Two revolutionary things, with a strong influence on further electrochemical engineering
development and electrochemistry technology, also happened in the field of materials engineering
during the ‘60s:
 dimensionally stable anodes (DSA) were introduced in 1968 in industrial practice, providing
many advantages over the existing electrodes at that time, first of all a lower cell voltage,
thus making a great contribution in energy saving, and better anti-corrosive features, thus
having a longer lifetime;
 a co-polymer, having ionic features (ionomer) was synthesised and patented in 1966, called
NAFION and, due to its ability to conduct protons, it was considered and applied first as a
proton exchange membrane (PEM) in fuel cells and later in many other electrochemical
technology areas (chlor-alkali electrolysis, water electrolysis, metal electrowinning,
electroplating, electrodialysis, sensors and battery fabrication, ...), mainly for dividing the
anode from the cathode chamber in various electrochemical reactors. These two discoveries
had a great influence on the philosophy of thinking of scientists and engineers, opening up
new frontiers in the design and development of electrochemical cells and processes.
4. Growth (expansion) of electrochemical engineering as a science and art from the ‘70s till the
end of the ‘90s
Through these three decades of electrochemical engineering growth, several directions were
profiled and developed, mainly simultaneously. These directions are:
 Electrochemical reactors – development, modelling and optimisation;
 Electrochemical processes – improvements of the existing ones, and research and
development of new ones;
 Interconnection of electrochemical engineering with other sciences, in some cases forming
new scientific sub-disciplines;
 Publishing affairs – education of new generations in the electrochemical engineering
community.
4.1. Electrochemical reactors research and development
During the ‘70s and ‘80s electrochemical engineering had a very fruitful and progressive period
contributing to electrochemical reactor engineering development, which resulted in new
electrochemical reactors, as well as new electrochemical processes that appeared and found their
place in electrochemical technology. One can say that the ‘70s and ‘80s were the peak of the
electrochemical reactor research and development, when a lot of new cells appeared. Some of
them were developed on an industrial scale and marketed in that period, as:
 “Chemelec” cells (already mentioned) for metal removal from rinse and wastewaters;
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 Filter press cells for multipurpose use, either in mono- or bipolar mode (applied in water
electrolysis, in electrowinning, in electro-organic synthesis, known as ICI Cell, or SU Cell);
 Swiss-roll cells employed in the electro-organic synthesis of vitamin C in the period when
anodic oxidation had still to play a role;
 Pump cells;
 Capillary-gap mono- or bipolar cells, also for multipurpose usage;
 Rotating cylinder and rotating drum cells, both used for silver removal from spent photochemicals;
 TDE cells either as a fixed bed cell, such as an en-Viro cell, or as a fluidised bed cell for heavy
metal ions removal from various industrial effluents;
 Cylindrical cells with coaxial electrodes configuration and TDE anodes used in the NALCO
process;
 Bipolar trickle bed cells for electro-organic synthesis, as well as some others that can be found
in the relevant literature that have found their use for all the aforementioned purposes [6].
Particular attention in that period was paid to the TDE cells with fluidised bed cathode and enViro cells, considered as a new very promising and very powerful electrochemical reactor. Very
quickly after the first papers were published on the subject of TDE cells, a pilot-plant for the
fluidised bed cell was constructed by CJB Developments UK in 1972, and afterwards the first
industrial plant was built in 1978 in Germany by AKZO Zout Chemie Netherlands, only to be closed
a few years later, having exhibited certain disadvantages [7]. Later, during the ‘90s, thanks to the
appearance of advanced conductive materials with a very developed surface area and high
porosity, a new generation of TDE cells, including the Poro-cell, Reno-cell, and Retech-cell, was
developed and marketed. Although these cells were originally investigated and developed mainly
for metal recuperation from various industrial waste solutions containing a low level of metal ions,
sometimes a few p.p.m. only, they were later modified and used for electro-generation of
different oxidants used for oxidation of different organic or inorganic compounds.
The theoretical knowledge and laboratory experience in electrochemical reactor engineering
accumulated in that period contributed significantly to producing an optimal version of some of
these cells on an industrial scale.
In fact, scientists working in electrochemical reactor engineering were faced with the problem
of how to explore in the best way a simple relationship connecting the cell productivity with other
variables affecting it. Cell productivity per unit of installed volume and unit of time (termed also as
space-time yield [8]) is defined by the basic, well-known equation:
1 dm
 e kL aMcb (t )
V dt
(4)
where: ηe is the current efficiency; α = i/iL – ratio between operating and limiting current
density; a = A/V – specific surface area (working electrode surface per unit of cell volume); kL mass transfer coefficient; M – molar mass; cb(t) – concentration of metal ions in the bulk.
It follows from Eq. (4) that, for a given and constant bulk concentration cb(t), as is usually the
case in effluent and wastewater treatments, there are three possibilities for an increase in the
limiting current density as a measure of the maximum cell productivity:
A. to increase the mass transfer coefficient;
B. to increase the specific surface area of the working electrode; or
C. to increase both the mass transfer and specific electrode surface area in the same cell.
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A: Mass transfer around an electrode can be enhanced by making and keeping forced
convection in a cell. This can be carried out by:
1. changing the electrolyte flow conditions around working electrodes by either pumping or
stirring, or using an ultrasound source; rotating, shaking or vibrating a working electrode,
or in some other way;
2. introducing different ITPs in the inter-electrode space that will locally change electrolyte
flow close to the electrode surface;
3. bubbling gas around the electrodes.
All three methods of mass transfer enhancement were extensively investigated and the
contribution of each of them was quantified by scientists through the ’60s and particularly the
‘70s.
B: Specific electrode surface (a) area can be increased by:
1. decreasing the inter-electrode distance;
2. using either dispersive or porous conductive material connected with a current feeder as
a working electrode (TDE).
C: A cell with a TDE fulfils both requirements – it has a high specific surface area and, at the
same time, it has good mass transport properties independently, whether electrolyte flows by, or
through, the TDE. This aspect of enhancing the productivity of a TDE cell particularly occupied the
attention of scientists at that time, resulting in many papers relating to this issue.
Table 1 presents an approximate specific surface area and corresponding maximum space-time
yield (productivity) for different cells as an illustration supporting the statements made in the
previous text, but also to demonstrate an appreciable progression in designing a cell of high
performances.
Table 1 Specific surface area and maximum productivity of some particular cells
compared under similar operating conditions [7]
Specific surface area, m-1
Productivity at α =1, mol m-3 h-1
7.5
0.14
Filter press cell
30 – 170
0.56 – 3.17
Capillary gap cell
100 – 500
1.9 – 9.33
Fixed bed cell
1000 – 10 000
18.65 – 186.5
Fluidized bed cell
1000 – 10 000
37.3 – 186.5
Rotating drum cell
50 – 5000
9.32 – 93.3
Type of cell
Conventional cell
It is important to emphasise that, when the bulk concentration in Eq. (4) is time-dependent
(metal removal, for example), the current efficiency - ηe is also a complex and time-dependent
variable, depending, among other things, on the galvanostatic or potentiostatic mode of
operation. Numerous papers on the modelling and optimization of electrochemical reactors were
published at that time and later, in order to achieve the best working conditions, i.e., the highest
cell productivity at optimum energy consumption for not only the cells considered in Table 1 but
also for others. These papers made a great contribution to the development of electrochemical
reactor theory and engineering practice.
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4.2. Establishing new and improving the existing electrochemical processes
Thanks to the achievements in developing the new electrochemical reactors that are the core
of every electrochemical process, great success was attained in developing new processes and
technologies and in improving the existing ones.
i. A particularly significant contribution was made in electro-organic synthesis, where various
organic compounds were produced electrochemically on an industrial scale, such as:
tetraethyl lead, sorbitol/mannitol, glyoxylic acid, methoxy-benzylalcohol, adiponitrile,
methoxy-benzaldehyde, methylethylketone, propiolic acid, anthraquinone, naphthoquinone
and others. Many other organic products are under research and development on a pilot
plant scale and many more are still on a bench scale and will be commercialized soon.
ii. In electrochemical metal surface treatment, comprising electro-coating, electro-polishing,
electro-sinking and grinding, many new electrochemical tools and new electrolytes were
developed and commercialised. Great success was achieved in electroforming, where
numerous micro-products appeared, and various micro-fabrication methods were developed
and marketed. Micro-reactor technology was one of the more propulsive areas, and very
promising for the electrochemical production of some special chemicals in very small
amounts. In that period – the early ‘70s – the so-called LIGA process had already been
developed and employed, spreading its role into many areas of present day techniques and
technologies: in micro-mechanics, micro-acoustics, micro-optics, in information
technologies, in biotechnologies, biomedicine, and many other areas.
iii. The principle of the fuel cell (FC) was first described by W. R. Grove in 1839. Since then,
many efforts have been made and many types of FCs have been considered for producing
energy at low or high temperatures using mainly hydrogen as a fuel but also natural gas and
coal gas, in a mixture with hydrogen or alone. The greatest improvements in development of
proton exchange membrane (PEM) FCs capacity was achieved during the ‘90s. An almost 25fold increase in output power was achieved in that period, starting from 70 kW m-3 in 1989
and reaching 1.8 MW m-3 in 1997. This leap was a consequence of the increased interest of
the automotive industry, backed with adequate financial support, and was due also to new
catalytic materials and cells development.
iv. In parallel with FC developments, electrochemical engineering contributed a lot to
developing new and improving the existing water electrolysis and hydrogen production
technologies. The improvements of alkaline water electrolysis technology consist mainly in
improving the electrolytic cells to have an increased specific surface area; using advanced
materials as separators has led to a reduced inter-electrode gap, thus reducing specific cell
resistance. This, coupled with an increased operating temperature, as well as the
introduction of new catalytic materials, makes the whole process more energy/economy
viable. Besides these improvements, new technologies were developed in that period, based
on Nafion membranes offering qualitatively new approach to hydrogen/oxygen production
as well as water steam splitting on oxide ceramic.
v. Several substantial improvements were made at that time in chlor-alkaline electrolysis in
that period (from the ‘70s till the end of the ’90). The most important was substitution of
graphite with DSA, thus prolonging the anode life-time many times and preserving lower
chlorine evolution overpotential. The other improvements were similar to those applied in
water electrolysis, and relate to decreasing the inter-electrode space of electrolysers; mono-
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or bi-polar mode of operation; and substitution of amalgam process by diaphragm and
membrane processes, thus making the whole technology more environmentally sustainable.
4.3. Electrochemical engineering and other disciplines
The period between the ‘70s and the end of the past century was also characterized by the
penetration of electrochemical engineering into or interconnection with other disciplines. Here we
will discuss only those that I consider to be the most important. The others will only be touched
upon.
Extractive metallurgy
Electrochemical engineering has particularly contributed a great deal to the development of
hydrometallurgy, which also made its own very substantial progress during the ‘60s and on, of the
past century. Now, electrowinning is usually the last link in the technology chain for production of
various metals from ores by leaching followed by solvent extraction/ion exchange and an
electrowinning pathway. As a response to a significant growth in the theoretical knowledge and its
experimental confirmation, many attempts were also made in that period to improve the existing
or establish new purely electrochemical or metallurgical processes, as well as processes linked
with other adjoining disciplines. We will mention here only those processes and technologies
relating mainly to metallurgical engineering and environmental processes - the fields I am more
familiar with:
 Copper electrowinning from pregnant leach solutions, namely, the leaching-solvent
extraction-electrowinning (L-SX-EW) process of copper production, as a qualitatively new
technology was introduced on an industrial scale at the end of the ‘60s. As the major cost
component of this technology is the electrowinning step, which requires 8 to 10 times more
power than electrorefining, shortly afterwards many attempts were made with the aim of
making electrowinning less expensive and more efficient. One approach was an attempt to
replace the anodic reaction of O2 evolution by SO2 oxidation at copper or zinc
electrowinning, which would be a great step in making the process more economically
acceptable than it is now. So far, it is still at a development level. Another interesting
attempt was to carry out the electrowinning from an electrolyte containing cuprous instead
of cupric ions, thus cutting significantly the energy costs. Another interesting process is
electrolytic production of metals from corresponding sulphide mattes cast and served as
anodes in electrorefining plants. So far, only in nickel metallurgy has such an approach been
successfully implemented.
 The improvements made in extractive metallurgy of basic heavy metals were implemented
in some other technologies, in which electrowinning is the final step;
 Replacing the cementation processes by direct electrowinning in zinc electrolyte purification
from other metal ions using advanced cells based on TDE, prior to the zinc electrowinning;
 Recuperation of metals from spent electroplating baths, from spent solutions in electronics,
from spent pickling solutions in the metal working industry, from mother solutions in salt
production and from some other similar effluents that are produced in metallurgy or the
inorganic chemical industry;
 Electrolytic metal powder production is nowadays an important segment, providing starting
materials for sinter metallurgy, as well as in electronics, in metallic pastes production and for
many other products;
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 Applying different electrochemical coating and surface finishing methods leads to minimising
the corrosion effects in wastage of materials, to which electrochemical engineering
contributed greatly in the past and still currently does.
 Organic chemistry and organic chemical technology (electrochemical reactor design for
massive production; micro-reactors design and implementation for production of very
hazardous chemicals).
Environmental protection
In that period (‘70s to ‘90s), particular attention was given to environmental pollution and
environmental protection, due to an increasing demand for environmentally sustainable chemical
processes. As an answer to this demand, electrochemical engineering opened a new direction in
the treatment of different industrial effluents. Coming into this important and broad area,
electrochemical engineering started to play a key role in different aspects of pollution abatement,
in both aqueous and gaseous phase. Electrochemical methods and devices were developed and
employed for wastewater purification, either for removal of hazardous heavy metal ions from
them or for cyanide or chromate destruction; for direct anodic destruction of organic species that
must be destroyed prior to releasing such wastewaters into the recipient; for “in situ” water
disinfection for human usage or for special purposes.
Nowadays, also thanks to the development of advanced materials, boron-doped diamond
(BDD) anode is an industrial reality in drinking and wastewater treatment processes, and
particularly useful for anodic destruction of those organic pollutants from wastewaters that can
only be decomposed into less hazardous or even inert compounds at higher overpotentials with
no water electrolysis [9].
Electrochemical engineering has found its place also in off-gas cleaning technologies for either
direct electrochemical or indirect (using a proper electrochemically generated red/ox mediator)
conversion of harmful gaseous off-gas stream constituents such as: SO2, H2S, NOx, ammonia, Cl2,
amines, hydrocarbons and other organic constituents, previously absorbed by a proper absorbing
solution, from off-gas streams. So, for example, different variants were considered and developed
for SO2 removal from flue gases and its oxidation by an electro-generated oxidant (Ispra-Mark 13),
using a proper redox pair. A similar concept was also considered for NOx and SO2 removal from
gaseous mixture via absorption and oxidation of absorbed species by Ce4+ ions electrochemically
generated in a separate electrochemical reactor. An interesting and promising approach to direct
gas purification from organic and nitrogen compounds is the electrochemical catalyst promotion,
known also as NEMCA. By polarising a catalyst layer deposited onto solid electrolyte, its catalytic
activity increases 10 to 100 times. So far this method is still at the laboratory and bench scale.
Soil remediation is another area where electrochemical engineering has found itself
contributing significantly to resolving the problem of the purification of soil polluted by previous
industrial activities.
Recycling technologies
Following the concept of “zero discharge effluent technology”, electrochemical engineering
found its place in different recycling technologies, as an ultimate stage, for reclaiming and
recovery of useful or harmful metals from different waste devices such as: spent batteries, printed
boards and other electronic scrap –the amount of which grows ever greater; for metals removal
from spent electroplating baths, as already discussed; from spent pickling solutions; from mother
liquors; from spent photo-chemicals, different rinsing waters and other similar liquid sources.
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Significant results were achieved in the recycling of acids and alkalis by splitting corresponding
salts from large volume solutions produced in chemical industry or in metallurgy by means of
electrodialysis or a combination of membrane and ion-exchange resin techniques assisted by
electrochemical regeneration of loaded resin.
Wastewater purification and recycling in a process is in many cases more economically viable
than to treat it to a purity level tolerable to be discharged into a recipient. Besides removing metal
ions or destroying organic molecules, new electrochemically assisted techniques were developed
and included in technologies for removal of fine suspended particles from rinse waters such as:
electro-coagulation and electro-flotation, both efficiently employed on an industrial scale.
Some of the above-mentioned processes or technological innovations were developed and
marketed, while others remained only as an attempt on a laboratory or pilot-plant scale waiting
for further research, or were completely abandoned.
Other areas
Electrochemical engineering also penetrated the medical sciences, contributing to developing
new medical tools, new devices, new indicators, new drugs, new compatible materials for
orthopaedic purposes, for example, and many others.
In biochemistry, thanks to close collaboration with electrochemistry and electrochemical
engineering, a new sub-discipline has appeared recently, named bio-electrochemistry, where a lot
of new projects have been driven in developing new alternative sources for green energy
production, such as bio-fuel cells; for promoting or inhibiting bacterial activity and its proliferation;
for bioelectrocatalysis and for similar purposes using small currents to manage the bacterial life
and features.
Obviously the three decades of the past century we have considered were very productive for
electrochemical engineering science, as well as for electrochemical engineering technology.
4.5. Education of new generations of electrochemical engineers
Due to a significant increase of papers relating to electrochemical engineering subjects, a strong
need appeared, at the end of the ‘60s, to establish a new, specialized journal for publishing such
articles. So, the first issue of the Journal of Applied Electrochemistry was published in 1970 [10].
In 1974, based on many theoretical and experimental contributions in electrochemical
engineering, Electrochemical Reactor Design, written by D.J. Picket, was published as the first
book on this subject. Later, several books with the keyword electrochemical engineering in their
titles appeared, with the aim of spreading the basic principles of the new science among younger
scientists and students studying chemical and metallurgical engineering. Some of the writers of
these textbooks, who significantly contributed to the development of electrochemical engineering,
are listed here chronologically as their books appeared: F. Coeuret and A. Stork (1984), I. Roushar
(1986), E. Heitz and G. Kreysa (1987), T. Fahidy (1988), K. Scott (1991), F. C. Walsh (1993), H.
Wendt and G. Kreysa (1999).
At that time (the early ‘80s) the first scientific symposium entitled Electrochemical Engineering
was held at Loughborough University UK, as a response to the increased interest in presenting the
research results amongst a specialised group of scientists. After this first attempt, the next
symposia were held every three years, always at Loughborough. These events were a good
indicator for identifying major areas of research interest and key directions which electrochemical
engineering had moved towards, in the period between two events.
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In the meantime, the EEWP (Electrochemical Engineering Working Party) was constituted as a
branch of the EFCE (European Federation of Chemical Engineers).
Following a successful tradition of organizing electrochemical engineering symposia, the EEWP
took over this duty from Loughborough University, and the 1st European Symposium on
Electrochemical Engineering was organized soon after in Bad-Soden, Germany, in 1990. The 9th
was held in 2011 in Patras, Greece. Besides this symposium, held every three years and having a
European character, similar symposia are organized in the frame of world meetings such as ISE
Annual meetings and CHISA congresses, allowing the gathering of scientists from other parts of the
world to present their results.
Also, taking care of the young scientific population interested in coming into electrochemical
engineering science, the European Summer School on Electrochemical Engineering was held for
the first time in Toulouse, France in summer 1995 and thereafter in Ferrara, Italy; Patras, Greece;
then in Palić, Serbia and most recently in Almagro, Spain, in 2009.
5. Electrochemical engineering at the end of the first decade of 21st century
Electrochemical engineering has extended far beyond the limits which were drawn by the early
works in the ‘60s when the main theme was the mass transport of ions to or from an electrode.
One can still occasionally find in the literature papers concerning this subject, but this is rather a
reflection on the works done during the ‘60s to ‘80s. Such papers are mainly directed towards the
corrosion process induced by mono- or two-phase flows. The published relationships at that time
on mass transfer in electrochemical systems can today cover any particular technical problem.
Also, current density distribution is something that can be routinely solved employing modern
computational techniques and reliable numerical methods. With these tools, modelling of any
electrochemical reaction system with mono- or two-phase flow of electrolyte and a dispersed gasor solid phase in a cell with or without separator is now possible and something that can be
successfully used in everyday practice. In these circumstances, what does electrochemical
engineering at the end of the first decade of the new century mean? What is the role of the
electrochemical engineer in following the established principles and in finding challenging new
subjects and directions for further upgrading electrochemical engineering science? It may sound
too declarative, but the following text could be an answer to the above questions:
“It is the responsibility of the electrochemical engineer in industry to simultaneously
manage electrical consumption and chemical production. He or she must apply relevant
scientific and engineering principles to design, construct, and operate a process in an
economical, safe, and environmentally conscious manner. Improved understanding of
scientific principles and the application of new materials can lead to more efficient cell
designs and processes. The constant evolution of technology provides challenging and
rewarding careers to engineers and scientists in a range of disciplines. Among the
considerations that influence cell efficiency and lower consumption are temperature,
spacing between electrodes, electrode material, electrolyte consumption, cell size,
source of raw material, and production rate. Clearly, engineering skill is required for
understanding these effects and for achieving optimum production conditions”.
From “Industrial electrolysis and electrochemical engineering”
by M. Grotheer, R. Alkire and R. Varian [10].
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J. Electrochem. Sci. Eng. 2(2) (2012) 53-66
6. New challenges and frontiers in electrochemical engineering [11]
According to the last sentence from the cited text, there will be a great period for further
development of electrochemical engineering.
Indeed, one should expect the further influence of electrochemical engineering on
improvements of existing electrochemical technologies, and development and establishment of
new ones that are still on the laboratory scale. Some of them have already been mentioned in the
previous sections.
In the past, electrochemical engineering faced much more towards electrochemistry and less
towards chemical engineering. Closer collaboration with the second science has to be established
in the future, particularly in solving problems arising in cell scaling and optimisation, and
particularly those with three-dimensional electrodes (their implementation in different separation/purification processes is not as expected), as well as those with membrane processes.
Knowledge about transport processes across membranes, for example, is not complete yet, in
spite of the fact that many industrial membrane processes exist.
How to design and construct more efficient cells and large processes for electrowinning of
copper to work at lower specific energy consumption? Few new hydrometallurgical processes are
at present under development. The question is when they will be marketed. Each of them has
metal electrowinning as the last stage in the whole technology chain. The contribution of electrochemical engineering to research and development of these processes could be extremely
valuable.
How to design cells and the process for electrorefining of metals to improve their purity? In this
view, fundamental principles of thermodynamics, kinetics, hydrodynamics, mass transport and
potential and current distribution have to be transformed into engineering concepts in order to
achieve economical operation and high quality products, lessening impurities into deposit as much
as is permitted.
The contribution of electrochemical engineering to the research and development of these
processes could be very valuable.
How to make fuel cells less expensive for wider applications? This is mainly connected with the
kind and amount of materials to be built in, but also with fuel cells design and their scaling, with
fuel production and storage and with many other things, which electrochemical engineering may
contribute towards. How to make fuel cells capable of operating and surviving in extreme conditions?
What has electrochemical engineering still to do in the pollution abatement area? How to
achieve a zero discharge of pollutants in both gaseous and liquid exit streams? Beside improvement of the existing technologies, a problem with the existing relationships, describing kinetics
and thermodynamics, and with their validity at concentrations approaching zero, needs to be
reconsidered. This is a great challenge on the theoretical level. Many opportunities exist in areas a
few of which are listed below:
 Wider application of BDD electrode in wastewater treatment can be expected, which will
allow a successful anodic destruction of hazardous organics from wastes.
 Electrokinetic soil remediation is an emerging technology that has attracted increased
interest among scientists and officials because of its great potential.
 It can be expected that electrochemical promotion of catalyst (NEMCA effect) should
emerge from the laboratory scale, turning a new page in exhaust gas purification.
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 The appearance of room temperature ionic liquids (RTIL) opens new opportunities where
electrochemical engineering has to find its place and role in establishing new processes
based on a new approach.
How can electrochemical engineering contribute in materials recovery, waste minimisation and
recycling? This problem is an area where electrochemical engineering is already involved, but it is
also an area where there are a lot of still unsolved problems. In particular, this relates to the
recycling of electronic devices and scrap and the recovery of valuable materials.
What could bioelectrochemistry and bioelectrochemical engineering, as sub-disciplines
undergoing very fast development, do to establish new electrochemical processes, products and
cells for different purposes?
What more can electrochemical engineering do in and for nano-technologies?
What should be next? Where then is the limit? I do not know. Do you?
In the end, what does electrochemical engineering mean nowadays compared to the definition
given below the title, provided almost half a century ago? Do we have to redefine it according to
the current state?
Acknowledgement The author would like to express his gratitude to F. C. Walsh, G. Kelsall and F.
Lapicque for their suggestions, help and useful critiques in composing this paper.
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© 2012 by the authors; licensee IAPChem, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
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